Hadron Spectra and Yields Experimental Overview

Hadron Spectra and YieldsExperimental Overview

Julia Velkovska

INT/RHIC Winter Workshop, Dec 13-15, 2002

INT/RHIC Winter Workshop 2002

Julia Velkovska (BNL)2

Outline

Spectra Radial flow Does every particle flow ? What are the freeze-out conditions ?

Yields and Ratios Chemical properties of the system Is Tch > Tfo ?

How far in pT do soft processes dominate ?

Conclusions



Charged hadron spectra at 200 GeV

Exponential at low pT < 2 GeV/c

Power-low at high pT > 2 GeV/c



Spectral shape evolution with centrality

pT < 2 GeV/c

Inverse slope increases with centrality due to radial flow

Relatively little change from 0 – 50 % pT > 2 GeV/c

Suppression of high pT hadrons increasing with centrality



P spectra from Star

High quality data over 9 centrality selections

Shape described by

blast wave fit



Spectra with broad momentum range from PHENIX

0 – 5 % 5 -10 %10- 15 %15 – 20 %20 – 30 %30 – 40 %40 – 50 %50 – 60 %60 – 70 %70 – 80 %80 – 93 %

Au+Au at s = 200 GeV PHENIX preliminary



The general features

Peripheral : ~ equal slopes Pions dominate

over (anti)protons at all pT

Central low-pt slopes

increase with particle mass

proton and anti-proton yields equal the pion yield at

high pT



Comparison for 200 GeV central data from all RHIC experiments

Relatively good agreement on preliminary data

Low pT data from PHOBOS will help constrain extrapolations to pT = 0 GeV/c



Characterizing the expansion

Strong radial flow: Spectra are NOT

exponential in mT

Inverse slopes depend on fitted (measured) range

Curvature increases with particle mass

At high mT all spectra converge to the same slope

< pT > versus mass – better than Teff versus mass, but still depends on fit function – very low pT data helps

1/m

T d

N/d

mT

(a.u

.)mT-m

mass



<pT> versus mass

M. Kaneta/N. Xu (STAR)

<pT> prediction with Tth

and <> obtained from blastwave fit (green line)

<pT> prediction for Tch = 170 MeV and <>=0pp no rescattering, no flowno thermal equilibrium

STAR

preliminaryF. Wang

<pT> of and from exponential fits in mT

Do they flow ? Or is <pT> lower due to different fit function?



Fits to Omega mT spectra

M. van Leeuwen (NA49)

• At SPS and are now found to be consistent with common freeze-out• Maybe and are consistent with a blastwave fit at RHIC• Need to constrain further more data & much more for v2 of

C. Suire (STAR)

SPS/NA49

RHIC

STAR preliminary

T is not well constrained !



<pT> systematics: centrality and beam energy

open symbol : 130 GeV data

•Systematic error on 200 GeV data (10 %), K (15 %), p (14 %)

<p

T>

[G

eV

/c]

<p

T>

[G

eV

/c]

• Increase of <pT> as a function of Npart and tends to saturate < K < proton (pbar)• Consistent with radial flow increasing with beam energy and centrality• But also can come from initial state multiple scattering or gluon saturation.



Kinetic freeze out parameters

From hydrodynamics fit

Au+Au at sqrt(sNN) =200GeV

Top 5% centrality:

STAR:

Tfo ~ 100 MeV

T ~ 0.55c (130) & 0.6c (200)

PHENIX:

Tfo ~ 121MeV(130) &110 MeV(200)

T ~ 0.47c (200)

Full model calculations give similar results



BRAHMS, submitted to PRL12/07/02 nucl-ex/0207006

Becattini: T=170, s=1

PBM (PhysLettB518

(2000)41) predicts y=0

ratios almost exactly

K-/K+=

exp(2s/T)(pbar/p)1/3

K- /K+=(pbar/p)1/4 is

a fit to the data points

Thermal parameters from K-/K and pbar/p ratios



The chemistry of the collisions

Thermal models work well in describing particle ratios, even for the multi-strange particles : Tch

= 177 MeV – close to critical temperature



Short-lived resonances : a measure for rescattering timescale

Chemical freeze-out

Kinetic freeze-out

K*

lost

K*

measured

K

K* K

K*

K*

K

K*

K K K*

measured

Consistent with sudden freeze-out



Is Tch > Tfo ?

Single freeze-out model: Broniowski,Florkowski hep-ph/0209286

2 thermal and 2 geometric (flow) parameters describe all central data including K*0 (892) How good is the

agreement really ? Plots of theory/experiment

on a linear scale ? Comparison to other

observables?



When does the flow start ?

P.Kolb and R. Rapphep-ph/0210222 Including pre-equilibrium

transverse flow field improves agreement with the data

centrality0-5%

20-30%40-50%



And how far in pT does flow dominate?

Fit the soft part of , K,p

spectra using hydrodynamics expression

h+ + h - = , K, p

Compare to measured non-identified charged data

Significant soft component up to 2.5 – 3 GeV/c

130 GeV PHENIX



Another approach: look for jet fragmentation ratios as seen in pp data

• Experimentally observed:

above pt=2 GeV/c particles are fragments of jets

• Characteristic particle

composition determined by

fragmentation function Soft to hard transition in p/

ratio



(anti)proton/pion ratio: Can we determine soft to hard transition?

Ratios steeply rising to pT ~ 2 GeV/c

Above pT = 2 GeV/c – flat ~ 1 for central Au+Au ~ 0.3 – 0.4 for peripheral Au+Au

Is there a peak ? At what pT do we get to the pQCD ratios ?



If protons are soft up to 4 Gev/c

R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominatesR< 1 at high-pT suppression

pp

centralbinarycentral

Yield

NYield / R=

pionsprotons

Tslope~ sqrt [ (1+<<

For mT > 2 m0

central

peripheral



Scaling the proton+anti-proton spectra

Radial flow

Collision scaling ?

Nbin

97542213514.8



How does the ratio Central/peripheral look ?

…. and more details See PHENIX talk by Jiangyoung Jia And overview talk by David d’Enterria



Conclusions

A wealth of spectra, yields, ratios measurements from the first 2 years of RHIC

Spectral shapes consistent with strong radial expansion

Success of thermal chemical models Almost net baryon free system with Tch close to

critical temperature

Resonance studies show time-scale for emission is short , Tch close to Tfo

Abundant protons+anti-protons at intermediate/high pT . How do they get there ?

Documents

Hadron Spectra and Yields Experimental Overview